Field of Invention
Various embodiments of the present disclosure relate to a remote inspection apparatus for a heating tube of a steam generator, and more particularly to a remote inspection apparatus for a heating tube of a steam generator capable of approaching inside the steam generator through a hand hole of the steam generator and inspecting a deposited state of foreign substance or sludge introduced into an exterior of the heating tube or into a gap between the heating tubes.
Description of Related Art
Generally, using a steam generator, a nuclear power plant generates the steam needed to produce electricity from a steam turbine and generator. In such a steam generator, a plurality of heating tubes may be arranged in bundles, each heating tube exchanging heat between primary water that includes radioactive material and secondary water that drives a turbine, and separating the primary water and secondary water from each other.
In a steam generating process, the primary water heated while passing through a reactor flows inside the heating tube of the steam generator while the secondary water is supplied to the exterior of the heating tube, and then the primary water and secondary water exchange heat through the wall of the heating tube. Then, the heat-exchanged primary water is circulated back to the reactor along a conduit of a closed circuit while the secondary water is converted into steam.
In the steam generator, since the primary and secondary water exchange heat through the wall of the heating tube, high temperature and high pressure radioactive water (primary water) flows inside the heating tube while nonradioactive water (secondary water) flows outside the heating tube. Therefore, in a case the heating tube is damaged, the radioactive water (primary water) inside the heating tube may leak outside the heating tube and mix with the nonradioactive water (secondary water), which may result in a serious problem of contaminating the entire area to which the steam converted from the nonradioactive water (secondary water) is supplied. Therefore, securing the integrity of the heating tube is dealt as the most important task in operating a nuclear power plant.
Hereinafter, the aforementioned steam generator will be explained in further detail with reference to the attached drawings.
FIG. 1 is a schematic cross-sectional view of an interior of a steam generator, and FIG. 2 is a schematic view illustrating an operational principle of the steam generator of FIG. 2.
Referring to FIGS. 1 and 2, the steam generator 10 may consist of an inlet nozzle 11 through which a primary reactor coolant enters, heating tubes 13 where heat exchange is conducted, and an outlet nozzle 12 that transmits the heat from the reactor coolant entering the inlet nozzle 11 to a secondary coolant. The heating tubes 13 are placed on top of a tube sheet 14, and the heating tubes 13 being supported by tube support plates 15 at every certain vertical height thereof. Between the tube support plate 15 and the tube sheet, a flow distributing plate 16 on a donut shaped plate is placed to support the heating tube 13. The plurality of tube support plates 15 spaced by a certain vertical distance that support the heating tube 13 and the heating tube 13 combines a wrapper 18 having an open lower part and a steam outlet 17 on its top end, the wrapper 18 playing the role of receiving water downwards along an inner wall of an external housing 19, and discharging upwards the steam generated from the supplied water by the heating tube 13.
In the steam generator 10, the primary reactor coolant enters the inlet nozzle 11, flows inside the plurality of heating tubes 13, passes through the outlet nozzle 12, thereby transmitting the heat to the secondary coolant outside, wherein steam is generated. In such a steam generator 10, the part where the reactor coolant flows is referred to as a primary side, and the part where the supplied water and steam flow is referred to as a secondary side. The secondary water may consist of main vapor water, turbine water, condensed water, and supplied water. The vapor generated at the secondary side of the steam generator 10 moves along a main vapor tube, thereby rotating the turbine.
Supply of the secondary water to the secondary side to generate steam in such a steam generator 10 is made through filtration and chemical treatment, but the secondary water is introduced into the steam generator 10 together with foreign substance and sludge generated through various routes while circulating inside the conduit, and is thus deposited on the tube sheet 14, tube support plate 15, and flow distributing plate 16, or stick to an outer wall of the heating tube 13, thereby deteriorating or damaging the heating effect. That is, the steam generator 10 is arranged as thousands of heating tubes 13 form bundles, and thus foreign substance or impurities introduced through various routes or generated as an operating fluid passes through may be deposited on the exterior surface of the heating tubes 13, which may not only deteriorate the heat exchanging capacity of the heating tubes 13 but also the foreign substance and impurities solidified as sludge may cause denting between the tube support plate 15 and heating tubes 13, damaging the heating tubes 13.
Therefore, removing scale from the surface of the heating tubes 13 and the sludge from the tube support plate 15 is becoming an essential means for securing the integrity of the heating tubes 13 and the efficiency of the steam generator. And for this purpose, various inspection facilities such as small endoscope cameras are being adopted to check the state of the flow distributing plate 16, heating tubes 13 and tune sheet 14.
For example, there is a well known visual inspection apparatus (so called, KIIS) developed by the applicant for inspecting gaps of heating tubes of steam generators. Such a visual inspection apparatus is configured to be inserted through a hand hole placed in a lower part of the steam generator. The visual inspection apparatus enters in a direction perpendicular to a divide plate as it moves along a circumferential direction using a space between the heating tube bundles and shroud, and a probe is inserted between the tubes to perform an inspection. However, in such a visual inspection apparatus, sagging may occur as a robot moves, due to gravity, and thus the apparatus requires constant correctional control, and not only that, it would take a long time to do the setting and to correct errors before moving along columns of the heating tubes and conducting the inspection, thereby deteriorating the operational efficiency.